A Study on the Removal of Pollutants from Wastewater by Aquatic Macrophytes

Transcription

1 Journal of the Korea Academia-Industrial cooperation Society Vol. 13, No. 2 pp , 12 A Study on the Removal of Pollutants from Wastewater by Aquatic Macrophytes Hae-Yong cho 1* 1 Dept. of Environmental Engineering, Sun Moon University 수생식물에의한폐수의오염물질제거에관한연구 조해용 1* 1 선문대학교환경공학과 Abstract Macrophyte plays an important role in purification of wastewater. They have capacity to improve the water quality by absorbing nutrients, with their effective root system. In this study, removal of nutrient as well as organic matter was observed by some important macrophytes i.e. Pistia stratoites, and. indepe ndently as well as in mixed culture under the laboratory condition. The highest total nitrogen removal was observed for Pistia stratoites (86.47%) in monoculture and. + P. stratoites (76.11%) in mixed culture system. Corresponding figures for total phosphorous were observed for P. stratoites (7.6%) in monoculture and Salvinia sp. + P. stratoites (71.11%) in mixed culture system. Similar result was observed for ammonia removal in both systems. Additionally, P. stratoites showed the highest removal of organic matter, in monoculture system (68.46%) where as. + P. stratoites showed the highest removal of organic matter in mixed culture system (82.73 %). 요약수생식물은폐수정화에있어서중요한역할을한다. 수생식물은뿌리로영양물질을흡수해수질개선을할수있는능력을가지고있다. 본연구에서는실험실에서수생식물인물상추, 자라풀, 생이가래를각각의수조와혼합한수조에서영양물질제거뿐만아니라유기물에관해관찰하였다. 단일수조에서가장많이제거된총질소는물상추가 86.47% 이고, 생이가래와물상추가혼합식재된수조가 76.11% 로관찰되었다. 총인의경우단일수조에서가장많이제거된것은물상추가 7.6% 이고, 생이가래와물상추가식재된수조가 71.11% 로관찰되었다. 암모니아제거의경우도두개의수조에서유사한결과가나타났다. 또한물상추식재된단일수조가유기물이가장많은 68.46% 로제거를보였다. 반면혼합수조에서는유기물의제거가생이가래와물상추가식재된수조가가장많은 82.73% 로나타났다. Key words : Aquatic macrophytes, Monoculture, Mixed culture, Nutrient removal. 1. Introduction The high productivity and pollutant removal capability of aquatic plants in wastewater treatment is well known[1]. Natural aquatic systems have created substantial interest regarding their potential use for wastewater treatment and resource recovery using green environments. Aquatic plant system has been accounted as one of the processes for wastewater recovery and recycling. The main purpose of using this system has focused on waste stabilization and nutrient removal. Plant assimilation of nutrients and its subsequent harvesting are other mechanisms for pollutant removal. Macrophytic vegetation plays an important role in maintaining the ecosystem. Various types of macrophytes emergent, free, floating, submerged are generally observed * Corresponding Author : Cho, Hae-Yong(chohy@sunmoon.ac.kr) Received December 6, 11 Revised (1st January 18, 12, 2nd February 2, 12) Accepted February,

2 한국산학기술학회논문지제 13 권제 2 호, 12 in an aquatic ecosystem. Free floating macrophytes in which leaves and roots are floating, roots are not attached in sediment. It has tremendous capacity of absorbing nutrients and other substances from the water[2] and hence brings the pollution load down. The macrophytes provide good conditions for physical filtration and a large surface area for attached microbial growth and activity[3]. Aquatic macrophytes can also utilize large amounts of N and P removal capacities of different aquatic plants [4,]. The nitrogen and phosphorous are considered to be the major inorganic nutrient elements for the promotion of plant growth. Macrophytes also have a metabolic role in wastewater treatment with the potential to release O 2 into rhizosphere aiding in nitrification and by the direct uptake of nutrients[3, 6]. The major ecological function of wetlands includes water purification, hydrological modification, protection against erosion and deposition, provide habitat for flora and fauna, aesthetic appeal and provide recreational opportunities[7]. The wetland system is energetically sustainable because it uses only natural energy to reduce pollutants. They not only assimilate pollutants directly into their tissues, but also act as catalysts for purification reactions by increasing the environmental diversity in the rhizosphere, promoting a variety of chemical and biochemical reactions that enhance purification[8]. Therefore, the use of wetland technologies is increasingly employed for wastewater treatment because of its positive greenhouse results, also its being relatively cost and efficient. Wetland plants play a wide range of roles in constructed wetlands for wastewater treatment. Roles includes the physical effects of the plants themselves in sedimentation, erosion control and providing surface area for microbial growth(bioflims), thus increasing microbial assisted processes including nitrification and denitrification. The objective of the current study was to compare the potential of three floating aquatic macrophytes in monoculture and mixed culture system, in removing the total nitrogen, ammonium nitrogen, total phosphorous and organic matter from domestic wastewater and to establish their role in improving water quality. Wastewater treatment in aquatic macrophytes system occurs by several mechanisms including solids settling, plant uptake of contaminants, biotransformation, and physico- chemical reactions. This paper compares the nutrient removal in mono and mixed culture system within the culture media for the selected floating aquatic macrophytes in laboratory condition on diluted domestic wastewater. 2. Experimental methods Study was designed to evaluate the nutrient removal capacity of selected aquatic macrophytes such as Pistia stratoites,. and. All the three plants were cultured individually (monoculture) with % cover and in combinations with equal coverage of the total surface area of aquarium by the two partners in mixed cultures[9]. Four sets of aquarium were set in laboratory having L of diluted wastewater; dilution was done by the addition of wastewater with tap water in a 1:1 ratio. The aquarium with no aquatic plants referred to as control set. Each aquarium was filled by L of diluted wastewater and losses in culture volume due to evapotranspiration was maintained by the addition of deionized water to the original level prior to the day of sampling so that deionized water additions would minimally impact measurements[]. The experiment was conducted over a 1 month period, during which observations were made of changes in appearance and growth of the plants. Through out the study the growth chamber was adjusted 24 temperature, 6% humidity and alteration of photoperiod(12h light and 12h dark). The treatments were evaluated by measuring the chemical parameters in grab samples. Samples were obtained by dipping a ml graduated beaker at the center of aquarium. Care was taken to minimize disturbance of the plants. The wastewater in each aquarium was sampled 9 times over a 32 day period, on days, 4, 8, 12, 16,, 24, 28, and 32. The parameters measured included chemical oxygen demand(codcr), total nitrogen(t-n), ammonium nitrogen(nh 3-N), total phosphorous(t-p). CODcr was determined by reactor digestion method with test kit. After mixing the kit was heated for 2 hour sat C in thermoreactor(model# WTW- CR-3). The sample was cooled down for ten minutes and measured the CODcr value in portable spectrophotometer(model# 942

3 A Study on the Removal of Pollutants from Wastewater by Aquatic Macrophytes HACH-DR-28) at 4nm. T-N was determined using the chromotropic acid method with test kit. The kits were shaked for 1-2minutes and heated for 3min at 1 C in thermoreactor(model# WTW-CR-3) and cooled down for minutes. The T-N was measured in portable spectrophotometer at 4nm(model# HACH-DR-28). Ammonia was determined by Nessler Method by using test kits. For the ammonia test 1ml filtering sample was added in the test kit tube and added 4 drop of solution S1 and 1ml of solution S2. The test kits were shaked for 1-2 minutes and hold for 3minutes. The value was measured by(model# HACH-DR-28) portable spectrophotometer at 4nm. T-P(filtered samples) was determined by Ascorbic Method with test kits. ml sample was put in test kit and powder P1 was added. The test kits were shaked for 1-2 minutes to dissolve powder. The kits having powder and sample were heated for 3min at 1 C in (model# WTW-CR- 3) thermoreacter. Test kits were hold for ten minutes at the room temperature and measured the removal of T-P value by (model# HACH-DR-28) Portable spectrophotometer at 88nm. showed that the plants were significantly more efficient compared with the control. In both of the system the rise of CODcr observed after two weeks. Our result confirmed that the growth of water lettuce (Pistia stratoites) individually and in mixed culture showed higher performance to remove CODcr mainly because of well developed root system which can hold the initially low level of CODcr. Similar result was observed by[11]. A major part of the degradation of pollutants in the wastewater is attributed to micro- organisms which may have established a symbiotic relationship with plants. CODcr(mg/L) 3 A Pistia stratiotes Results and discussion B Salvinia +Pistia 3.1 Variation of chemical oxygen demand Figure 1 A and B illustrated the changes of CODcr concentrations by considering the plant species and control experiment in monoculture and mixed culture systems. Initially the CODcr concentration of wastewater in monoculture was 2.mg/L, where as in mixed culture it was observed for 84.mg/L. After the treatment period of 32 days with Pistia stratoites showed 16.4 mg/l (86.66%) for the monoculture. Similarly, in mixed culture system it was observed for the mixture of Salvinia + Pistia, 14.mg/L (82.73%). Around % of the decrease in parameters occurred within the first 12 days of the experiment. This reduction was mainly brought about by sedimentation in the control system and additionally by filtration through the root systems in the plant cultures. An important consequence of figure 1 A and B showed that the first two week is favorable to get optimum removal of CODcr. Result also CODcr (mg/l) [Fig. 1] Variation of CODcr in control and planted experiment in monoculture [A] and mixed culture system [B]. 3.2 Nutrient removal The losses of nitrogen and phosphorous concentrations were observed to have close relationship with different plant species. Planted treatment showed the removal of T-N compared with control treatment. These T-N removal rates were significantly greater than those for control treatment. Removal of N occurred by plant uptake, microbial assimilation and denitrification processes. 943

4 한국산학기술학회논문지제 13 권제 2 호, 12 During present investigation the highest removal of T-N was recorded for Pistia stratoites(86.47%) in monoculture and the mixture of Salvinia + Pistia 76.11% was observed for mixed culture system. Physiology of plant such as height of plants and the shape of leaves also affected the overall nutrient in aquatic plant treatment[12]. In our experimental plants, the Pistia stratoites has the highest leaf area and biomass that is why in monoculture system Pistia stratoites and in mixed culture system Pistia + Salvinia showed the highest T-N removal as compared to other plant species. Removal of T-N also attributed by micro-organisms attach on the different parts of plant, they form a biofilm layer, which played an important role to removal nitrogen from wastewater[13]. This indicated that plant uptake is one of the major nutrients removal pathways. In addition to plant uptake, T-N removal can occur by NH 3 volatilization favored by high ph, nitrification under aerobic conditions and denitrification under anaerobic conditions and formation of organic films[14]. In the present study, T-N removal was occurred by volatilization because ph was higher than 7. Figure 2B and 3B showed the removal of ammonium nitrogen. In the monoculture system, Pistia stratoites was able to remove the ammonium nitrogen by 86.66% followed by Salvinia 79.62%. Similarly in mixed culture system, it was observed for the mixture of Salvinia + Pistia 71.28%. At the end of experiment the presence of plants significantly reduced the ammonium nitrogen from their initially low levels where as in the control the value was somewhat higher. It may be due to that in control system, nitrification probably did not occur due to the lack of support for the nitrifying bioflim to grow. In our experiment although, the diluted wastewater initially had low level of NH 3-N, the Pistia stratoites helped in further purification of water so we can consider this species to be a good water quality indicator. Phosphorous is needed for plant growth and it s required for many metabolic reactions in plants and animals. Plants, algal and micro-organisms all utilize P as an essential nutrient and contain P in their tissue[]. Figure 2C and 3C showed the removal of T-P in mono and mixed culture. In monoculture Pistia stratoites showed maximum removal of T-P by 7.6%, followed by 72.6% within a given time period. Similarly, in mixed culture, it was observed for the mixture of Salvinia + Pistia, 71.11%. In both of the cases plants are significantly more effective to remove the T-P as compared to the control experiment. Reduction of T-P may be due to uptake of soluble P, filtration of particulate matter through the roots, and settling. Although initial level of P was low but the plant like Pistia stratoites with a well developed root system further purify the diluted wastewater. Combinations of large leaf and small leaf aquatic macrophyte removed higher nitrogen and phosphorous. T-N(mg/L) NH3-N(mg/L) T-P(mg/L) A B C Pistia stratoites Pistia stratoites Pistia stratoites [Fig. 2] Variation of T-N [A], NH 3-N [B] and T-P [C] in control and planted experiment in monoculture. 944

5 A Study on the Removal of Pollutants from Wastewater by Aquatic Macrophytes T-N(mg/L) NH3-N(mg/L) T-P(mg/L) A B C Salvinia+Pistia Salvinia +Pistia Salvinia+Pistia [Fig. 3] Variation of T-N [A], NH 3 [B] T-P [C] in control and planted experiment in mixed culture system. 4. Conclusions Aquatic macrophytes showed the significant removal of nutrient as compared with control. Floating plant such as water lettuce (Pistia stratoites) showed the highest removal of nutrients (T-N and T-P) in monoculture. It may be due to well developed root system in Pistia stratoites which provide the good habitat for bacteria to enhance the nitrification and denitrification which result in higher N and P removal. Similarly, mixture of Salvinia + Pistia showed the highest removal of nutrient. Combination of large and small leaf aquatic macrophyte removed the higher nutrient. Therefore, Pistia stratoites and Salvinia combination may be more effective to remove the nutrient in diluted wastewater. References [1] Kadlec, R.H and R.L. Knight, 199, Treatments wetlands: Lewis Publishers; Boca Raton, Florida. [2] Boyd, C.E., 197, Vascular aquatic plants for mineral nutrient removal from polluted waters, J. econ. Bot, 24, 7 ~ 6. [3] Brix, H, 1997, Do macrophytes play a role in constructed wetlands in the Sustainable Landscape, Wiley, New York. [4] Hill, D.T., V.W. Payne, E.J.W. Rogers, S.R. Kow, 1997, Ammonia effects on the biomass production of five constructed wetland plant species, J. Bio. Tech., 62, 9 ~ 113. [] Lauchlan, H.F., M.C. Spring, S. David, 4, A test of four plant species to reduce total nitrogen and total phosphorous from soil leachate in subsurface wetland microcosms, J. Bio, Tech., 94, 18 ~ 192. [6] IWA,, Constructed wetlands for pollution control, Processes, Performance, Design and Operation. IWA specialist group on use of macrophytes in water pollution control, IWA publishing. [7] Jenssen, P.D., T. Maehlum, T. Krogstad, 1993, Potential use of constructed wetlands for wastewater treatment in northern environments, J. Water Sci. Tech., 28, 149 ~ 7. [8] Greenway, M., and A. Woolley, 1, Changes in plant biomass and nutrient removal over 3 years in constructed wetlands in Cairns, J. Water Sci. and Tech., 44, 33 ~ 3. [9] Tripathi, B.D. and A. Upadhyay, 2, Dairy effluent polishing by aquatic macrophytes. 377~38. [] Jing, S. R., Y.F. Lin, D.Y. Lee and T.W., Wang,, Nutrient removal from polluted river water by using constructed wetlands, 76, 131 ~ 13. [11] Zimmels, Y., F. Kirzhner, A. Malkovskaja, 7, Advanced extraction and lower bounds for removal of pollutants from wastewater by water plants, J. Water Env. Res., 79, 287 ~ 296 [12] Iamchaturapatr, J., S.W. Yi, J.S. Rhee, 7, Nutrient removal by 21 aquatic plants for vertical free surface 94

6 한국산학기술학회논문지제 13 권제 2 호, 12 flow constructed wetland, J. Eco. Eng.,29,287~293. [13] Polprasert, C., S. Kessomboon, W. Kanjanaprapin, 1992, Pig wastewater treatment in water hyacinth ponds, J. Water Sci. Tech., 32. [14] Breen, P.F, 199, A mass balance method for assessing the potential of artificial wetlands for wastewater treatment, J. Water Res., 24, 689~697. [] Silvan, N., H., Vasander, J., Laine, 4, Vegetation is the main factor in nutrient retention in a constructed wetland buffer, J. Plant soil, 8, 179~187. Hae-Yong Cho [Regular Member] Feb : BA. Dept. of Landscape Architechure, Sungkyun Kwan University. Apr. 199 : Master of Engineering. Dept. of Landscape Architechure, Technical University Berlin. Jul : Ph D. Dept. Environmental plan, Technical University Berlin. Mar ~ current : Professor, Dept. of Environmental Engineering, Sun Moon University <Research Interests > Ecology, Environmental Impact Assessment 946